Hepatitis C –UpdateLaboratory Issues Hema Kapoor MD. SM Virology Section Manager Bureau of Laboratories Michigan Department of Community Health
Available at MDCH Screening tests EIA Supplemental RIBA( Recombinant immunoblot assay) Nucleic acid Amplification tests Additional Tests Available Commercially CIA(Chemiluminescence's immunoassays) Quantitative RNA Tests Genotyping Core Protein Antigen Laboratory Tests for HCV
REPORT Negatives Screening Test for Anti-HCV* Positive EIA/CIA Test RIBA for anti-HCV OR Nucleic acid test for HCV RNA Negative Positive REPORT Positive Negative Indeterminate RIBA for anti-HCV REPORT REPORT REPORT Negative Indeterminate Positive REPORT REPORT REPORT Laboratory Algorithm for HCV Testing * HCV EIA 2.0 ( Abbott), HCV version 3.0 ELISA( Ortho), VITROS Anti-HCV
Anti-HCV EIA False Positivity* by Population Prevalence 100 HCWs Military STD Clients Pregnant Women 50 Percent False Positive Dialysis Transfused Injecting Drug Users NANB Hepatitis ALT 0 <5%10% 60% >90% Prevalence of HCV Infection Source: CDC * As judged by RIBA or NAT
Consistency of Reported Anti-HCV Results • Screening test positive signal to cutoff ratios* • Results above the cutoff should predict a true antibody positive • Only results below the cutoff would require supplemental antibody testing • Cutoff should perform the same regardless of the population being tested * Not intended for use in screening donors as provided by FDA guidance
Anti-HCV Test Versions Evaluated Ortho 3.0, RIBA 3.0 N=25,532 • High-risk • Hemodialysis patients • STD patients • HCWs • General population (NHANES IV) VITROS Anti-HCV (Ortho), RIBA 3.0 N=1326 • Clinical specimens (Hospital-based patients) • Low prevalence populations Abbott 2.0, RIBA 3.0N=8,754 • STD patients • Students
EIA Signal to Cutoff Ratio • Signal: Optical density (OD) value of the sample being tested. • Cut off: Mean absorbance of negative Control plus 0.600. Example: Sample ODCutoff ODS/CO 1.595 0.623 2.56 1.243 0.543 2.29 1.271 0.543 2.34 s/cut off (s/co)- 3.8
_ Proportion of Anti-HCV EIA* Screening Test Positive Results Testing RIBA Positive by Average S/Co Ratio Prevalence 4.3% 2.2% 0% * EIA 2.0 or EIA 3.0 Source: CDC. MMWR 2003;52 (No. RR-3).
> (n = 1184) (n = 142) Screening-test-positive s/co ratio Proportion of Anti-HCV CIA* Screening Test Positive Results Testing RIBA Positive by S/Co Ratio Prevalence * VITROS Anti-HCV assay Source: CDC. MMWR 2003;52 (No. RR-3).
Proportion of Anti-HCV EIA RR Results Requiring RIBA Based on S/CO Ratio <3.8and HCV Prevalence Source: CDC. MMWR 2003;52 (No. RR-3).
Use of EIA/CIA S/CO Ratio to Determine Need for Additional Routine Testing • Screening-test-positive samples with s/co ratios >3.8*/8† can be reported based on screening test • >95% will be RIBA positive. • Screening-test-positive samples with s/co <3.8*/8† require additional testing because most are falsely positive. • In high prevalence populations few in this range. • Limits cost while improving accuracy of reported results. * Applies only to Ortho 3.0 or Abbott 2.0 EIA † Applies only to Ortho Vitros CIA
REPORT Negatives Screening Test for Anti-HCV OR Positives defined by s/coratios* All positives Positives with highs/co ratios Positives with low s/co ratios OR REPORT RIBA for anti-HCV Nucleic acid test for HCV RNA Negative Positive REPORT Negative Positive Indeterminate RIBA for anti-HCV REPORT REPORT REPORT Positive Negative Indeterminate REPORT REPORT REPORT Laboratory Algorithm for Anti-HCV Testing and Result Reporting: MMWR 2003 * HCV EIA 2.0( Abbott), HCV version 3.0 ELISA (Ortho), VITROS Anti-HCV Source: CDC. MMWR 2003;52 (No. RR-3).
Repeatedly Reactive Anti HCV Supplementary serological confirmation testing was not performed on this specimen with a high serum to cut-off ration in accordance with CDC guidelines (MMWR, 52 RR03; 1-16). Appx 95% of specimens with a high serum to cut-off ratio confirm positive when tested in supplementary tests. The serum to cutoff ratio is not related to severity of disease or acute/chronic phase of infection. Supplementary testing is available only after consultation with Dr. Jeff Massey…
Advantages of Revised Laboratory Guidelines • Standard reporting of anti-HCV positive results. • Reliable Interpretation of anti-HCV results. • Ensure positive patients receive follow-up • Prevent unnecessary evaluation of “false-positives” • Low cost of additional testing • Better understanding of performance and interpretation
Implications • Patients and physicians can reliably interpret results • Further clinical evaluation limited to true positives • Limit psychological stress on patients who test falsely positive • Substantially improve ability to establish public health surveillance systems to monitor effect of prevention and intervention activities